It's not a myth.<quoted text>THC is not an additive - it's the active ingredient in weed. And yes, THC levels have been rising, but that's not from tampering or any adulterants being added, it's from improved cultivating techniques. And that doesn't make it any more dangerous, just more potent, so you simply have to smoke less to achieve the desired effect. You could smoke 20 joints and be fine (you'd be so high you'd want to die, but I mean fine as in "not dead").
As for people "spiking" weed with other drugs - yes, that's completely a myth. I'm sure that it has happened of course, but to say it's a widespread or even occasional phenomenon is simply wrong. It just doesn't make sense from a business perspective. Why give away free drugs at worst, or cut into your profit at best?
I once smoked weed laced with cocaine.
The strangest trip I've ever had.
I remember taking a shower, looking at the showerhead and seeing the rainbow colored water twirling and twisting at me.